Displays which may present numbers, letters and/or other symbols have got a fast growing use in many different connections. This has resulted in a need of different display types for different purposes.
For example for pocket calculators the requirements are that the switch-over time should be below 1 second, that readability should facilitate quick reading, that battery consumption should be low and that reading should be possible for all levels of ambient light, which are considered "bright". The type of display which best has fulfilled these requirements is liquid crystal displays. That type therefore has become increasingly dominating for this purpose.
For instance, for signs in public environments, e.g. at stations and airports, the requirements on symbol size, readability and independence of ambient light are very high, while the requirement of quick switch-over is considerably less than for pocket calculators. Therefore electromechanical displays are used in many applications.
A display utilization which at present is relatively rare but is expected to get a very fast increase is price-marking of merchandise, e.g. in the form of electronic shelf edge labels.
The requirements of price-marking displays differ in several aspects from the requirements of displays for other purposes.
The presentation of price-marking displays should be able to be changed in a simple way by signal transmissions from a central computer, which controls that the display presents the price, which is registered at the cash-desk. But changes of the price is performed relatively seldom, normally at an interval of more than a week.
Consequently, the requirement for switch-over time by a price-marking display is very low. If it is decided not to perform any price changes during hours of open shop, all price changes may be performed in the night, when the displays do have several hours for switch-over.
In contrary the requirement of low power consumption for unchanged presentation is very high. The displays should be able to be positioned at the shelf edges and operate for years without changes of battery, without any wire connections and without radiating electric fields, which may have undesired effects.
Also the requirements of good contrast and clarity are very high for electronic price marking labels. A display which should tempt buying should not annoy the customer by difficulties to be read.
A way to fulfil the requirements of low power consumption for unchanged presentation and of good contrast is to utilize an electrochemical display.
By drawing current, at selected segments, through a suitable electrolyte it is possible to achieve reversible changes of colour, which remain until a current is drawn in the opposite direction. Thus, in this way, by means of an electric signal, the colour of the elements of the display may be chosen.